Leaf traits in relation to crown development, light interception and growth of elite families of loblolly and slash pine
Daniel J. Chmura (1, 2, 3) and Mark G. Tjoelker (1)
1. Department of Ecosystem Science and Management, Texas A&M University, 2138 TAMU, College Station, TX 77843-2138, USA / 2. Institute of Dendrology, Polish Academy of Sciences, 62-035 Kornik, Poland / 3. Corresponding author () / Received June 6, 2007; accepted November 19, 2007; published online March 3, 2008
Summary
Crown architecture and size influence leaf area distribution within tree crowns and have large effects on the light environment
in forest canopies. The use of selected genotypes in combination with silvicultural treatments that optimize site conditions
in forest plantations provide both a challenge and an opportunity to study the biological and environmental determinants of
forest growth. We investigated tree growth, crown development and leaf traits of two elite families of loblolly pine (Pinus taeda L.) and one family of slash pine (P. elliottii Mill.) at canopy closure. Two contrasting silvicultural treatments—repeated fertilization and control of competing vegetation
(MI treatment), and a single fertilization and control of competing vegetation treatment (C treatment)—were applied at two
experimental sites in the West Gulf Coastal Plain in Texas and Louisiana. At a common tree size (diameter at breast height),
loblolly pine trees had longer and wider crowns, and at the plot-level, intercepted a greater fraction of photosynthetic photon
flux than slash pine trees. Leaf-level, light-saturated assimilation rates (Amax) and both mass- and area-based leaf nitrogen (N) decreased, and specific leaf area (SLA) increased with increasing canopy
depth. Leaf-trait gradients were steeper in crowns of loblolly pine trees than of slash pine trees for SLA and leaf N, but
not for Amax. There were no species differences in Amax, except in mass-based photosynthesis in upper crowns, but the effect of silvicultural treatment on Amax differed between sites. Across all crown positions, Amax was correlated with leaf N, but the relationship differed between sites and treatments. Observed patterns of variation in
leaf properties within crowns reflected acclimation to developing light gradients in stands with closing canopies. Tree growth
was not directly related to Amax, but there was a strong correlation between tree growth and plot-level light interception in both species. Growth efficiency
was unaffected by silvicultural treatment. Thus, when coupled with leaf area and light interception at the crown and canopy
levels, Amax provides insight into family and silvicultural effects on tree growth.
